Azalea plant named ‘Robleb’

ABSTRACT

A new and distinct variety of Azalea plant found as a seedling in a planned cross between the female Azalea ‘Red Slippers’ and the male  Rhododendron oldhamii  ‘Fourth of July’. The new variety possesses a unique blooming time and is superior in development of an upright, dense, globose shaped plant with attractive large single to semi-double red flowers.

BACKGROUND OF THE INVENTION

The present invention relates to a new and distinct variety of evergreen azalea of the genus Rhododendron and a member of the Ericaceae family. This new azalea variety, hereinafter referred to as ‘Robleb’, was discovered by Robert Edward Lee of Transcend Nursery in August, 1986 in Independence, La. ‘Robleb’ originated from a planned cross hybridization between two selected breeding lines in a controlled breeding program in Independence, La. The value of this new cultivar lies in its unique blooming period, bloom color, bloom form, bloom size, and growth habit.

Asexual propagation of the new plant by cuttings has been under Mr. Lee's direction at the same location. The new plant retains its distinctive characteristics and reproduces true to the type in successive generations. The plant cannot be reproduced true from seed.

SUMMARY OF THE INVENTION

The following are the most outstanding and distinguishing characteristics of this new cultivar when grown under normal horticultural practices in Independence, La.

1. The unique spring, summer, and fall blooming.

2. A red flower color Red Group 42B with dotting color Red Group 53B.

3. Large, single to semi-double flowers rangeing in size from 2½″-3″ in diameter.

4. Easily propagated with semi-hardwood cuttings in late spring through the summer.

5. Fast growth rate under normal fertilization and moisture conditions.

6. Upright, dense and globose in nature.

7. Good specimen plant.

8. Desirable in planters.

9. Makes a very good hedge or screen.

10. Very good foundation plant for large buildings.

11. Does well as an understory plant in a woodland garden.

12. Hardy to Zone 7.

13. Attracts butterflies.

DESCRIPTION OF THE DRAWINGS

This new Azalea Hybrid variety is illustrated by the accompanying photographic prints in which:

1. The photograph at the top of the sheet is a close-up showing flower, foliage, and stem color as well as flower size and form.

2. The photograph at the bottom of the sheet shows the dense, upright and globose growth habit of a young three gallon plant.

The colors shown are as true as is reasonably possible to obtain by conventional photographic procedures. The colors of the various plant parts are defined with reference to The Royal Horticultural Society Colour Chart. Description of colors in ordinary terms are presented where appropriate for clarity in meaning.

BOTANICAL DESCRIPTION OF THE PLANT

The following is a detailed description of the new variety of Azalea based on my observations made of 2 year old plants grown in 3 gallon containers in wholesale commercial production practices, in greenhouses, and in established landscape plantings in Independence, La.

Distinctive Characteristics: Characteristic ‘Robleb’ ‘Red Slippers’ Height (Mature) 4-5′ 2-3′ Width (Mature) 3-4′ 3-4′ Flower Diameter 2½-3″ 2½-3″ Flower Form Single/semi-double Single/semi-double Flower Color Red G. 42B Red G.47A Flowers per 2-3 2-3 Terminal Bloom Period April April> Bloom Period Late July>Frost May Petal Number 5-15 5-10 Hardy Zone 7 7 Stamen Number 5-10 5 Stamen Type Some Petaloid Some Petaloid R. oldhamii Characteristic ‘Fourth of July’ ‘R. oldhamii’ Height (Mature) 8-10′ 8-10′ Width (Mature) 6-7′ 6-7′ Flower Diameter 1¾-2¼ 1¾-2¼ Flower Form Single Single Flower Color Red G.39A Red G.39A Flowers per 2-4 2-4 Terminal Bloom Period Mid-May>Mid-June Bloom Period Late June>Frost Sporadic>summer Petal Number 5 5 Hardy Zone 7 7 Stamen Number 7-10 7-10 Stamen Type Non-Petaloid Non-Petaloid

The female, or seed parent, of ‘Robleb’ is the Azalea ‘Red Slippers’; a purplish red, single to semi-double, mid-season blooming, low compact grower. ‘Red Slippers’ is an unpatented Back Acres hybrid developed by B. Y. Morrison in Pass Christian, Miss. Mr. Morrison first introduced these hybrids in 1964. His work was based on an interest in late-blooming and double flowering clones. ‘Red Slippers’ is the result of the following cross: (‘Andros’×‘Parade’)×‘Keisetsu’. ‘Andros’ (unpatented) and ‘Parade’ (unpatented) are Glenn Dale Hybrids and ‘Keisetsu’ (unpatented) is a Satsuki Hybrid.

The male, or pollen, parent is Rhododendron oldhamii ‘Fourth of July’ which originated from a R. oldhamii seed lot collected in 1968 by Dr. Hsu of Taiwan University. The seeds were collected at 850 meters elevation on Mount Tai Tun in Taiwan. Soon after this John Patrick of Oakland, Calif. was visiting Taiwan collecting plant material of the Taiwanese Rhododendrons. He obtained a number of seedlings from Dr. Hsu and grew them in Oakland, Calif. In 1973, Dr. John T. Thornton of Franklinton, La. obtained one of the Rhododendron seedlings from Mr. Patrick. Dr. Thornton noticed in the next few years that this particular R. oldhamii plant was a perpetual bloomer from late June until frost on new growth. This plant produces two flushes of growth containing flowers. The second flush of growth overlaps the first flush producing a plant which blooms continuously. This differs from the species R. oldhamii which blooms from mid-May until mid-June and sporadically through the summer. Dr. Thornton subsequently named this plant R. oldhamii ‘Fourth of July’ in 1972.

The azalea ‘Fourth of July’ seems to be hardy to about 10 degrees F. (zone 7). Temperatures below this cause dieback, but the plant readily recovers and blooms profusely the following summer. R. oldhamii is less hardy at zone 8.

Robert Edward Lee's hybridization program was conducted with emphasis on species that are not commonly found in the genetic make-up of the present day hybrids. The ‘Fourth of July’ cultivar which Mr. Lee obtained from Dr. Thornton in 1981 is a heavy summer and fall blooming plant, not like the Rhododendron Species Foundation form. The flower buds form on new growth and start blooming about July 1. Mr. Lee used this cultivar to cross with existing hybrids which have a tendency to bloom in the fall and which are also fairly hardy. As expected the resulting seedlings are heavy summer and fall bloomers with very impressive spring blooms also.

CLASSIFICATION

Botanic: Rhododendron hybrid ‘Robleb’.

Form: Upright, dense, and rounded.

Height: 4-5′.

Width: 3-4′.

Growth habit: Upright, dense and globose. Fast growth rate under normal fertilization and moisture conditions.

Growth rate: In a period of six years from a rooted cutting the plant reaches a height of 3 feet and a spread of 2 feet. The growth rate is normally about 6 to 8″ per year; the plant reaches a height of 4 to 5′ at maturity while maintaining a dense habit due to the abundant branch development.

Foliage: Alternate, simple, evergreen, pubescent, elliptic, and varying in size from 1½″ to 2″ long and ⅝″ to ⅞″ wide. The margins are entire, with a petiole ⅛″ to ¼″ long. Midveins and laterals are impressed on the upper leaf surface and prominent on the underside. The base of the leaf is cuneate to attenuate and the apex is acute to mucronate. The upper surface of the immature leaves is dull, pubescent, and is Yellow-Green Group 144A and the underside is Yellow-Green Group 146D, pubescent, and matte. The upper surface of the mature leaves is Yellow-Green Group 147A, dull and slightly pubescent and the underside is Yellow-Green Group 146B, matte, and pubescent. New growth is pubescent. These hairs are initially soft and white and cover both sides of the leaf with a higher concentration on the petioles and veins. They are slightly curled, flat, and range in length from {fraction (1/64)}″ to {fraction (1/32)}″. As the growth matures much of the leaf pubescence is lost; however, the stems, petioles, and leaf veins retain this pubescence which becomes more setaceous and darker in color (Brown Group 200B) through the growing season.

In 1994, the date of initial spring growth was March 5, in Independence, La. After the initial spring flush there was almost continuous growth until that fall ending October 20, also in Independence, La. When grown in full sun, the internode length of this plant is ¼″ to ⅝″; when grown in light shade the internode length is ⅜″ to ¾″. As would be expected a plant grown in shade results in a taller, less dense plant with larger leaves.

The average length of terminal growth of the initial spring flush is about 5″ for a plant in full sun and about 7″ when grown in shade. This growth should not be trimmed since it will produce flowers starting in August. As the plant continues to grow through the summer and fall more flower buds are produced, which mature and bloom until frost. This remaining growth produces about 4″ to 5″ of height. As cool weather approaches, some of the flower buds become dormant. These buds bloom in April of the next year.

Stems: The young stems, petioles, and lower end of the mid-ribs are Greyed-Purple Group 184A and densely clothed with spreading white glandular hairs. The upper end of the mid-rib and veins are Yellow-Green Group 146C. As the stems mature they become Yellow-Green Group 152B and by the second growing season they are Greyed-Green Group 197B, glabrous and rugose. The pith is solid and uniform. Young and older stems are densely branched.

Buds: Tight buds at ½″ are ovate and acuminate Yellow-Green Group 146D with a hairy pubescence Brown Group 200A. The buds are borne in clusters of 2 to 3, and are sheathed by a pair of modified leaf bracts which are from ¼″ to ½″ long, persistent, and Yellow-Green Group 147A. The pedicel is ¼″ to ⅜″ long, pubescent, and Red Group 53B. The calyx is ⅛″ to ¼″ long, Yellow-Green Group 144C, funnel shaped, persistent, and pubescent. The five imbricated sepals are lanceolate and joined at the base to form a cup. As the buds swell the bud sheath matures to a Greyed-Orange Group 165A, falls off, and reveals the flower color Red Group 42B.

Flowers: Perfect, single to semi-double, Red Group 42B (upper surface and undersurface), glabrous, open funnel shaped, 2½″ to 3″ in diameter by 2¼″ to 2¾″ in depth, borne on current season's growth, non-fragrant; they last on the plant in the garden 5 to 6 days. There are five true petals which are fused at the base, elliptic, and have wavy margins. These petals are 1¾″ to 2¼″ long, ¾″ to 1¼″ wide, and have rounded apexes and entire margins. Three out of five petals are dotted with Red Group 53B. There are 5 to 10 non-petaloid stamens which are ¼″ to 1″ long. The filaments are Red Group 42A, the anthers are Red-Purple Group 59A, and the pollen matures to Yellow Group 11B. The 8 to 10 petaloid stamens are from ¼″ to 1″ long, ¼″ to ¾″ wide, and odd shaped. The margins are entire and the apexes rounded. The pistil is single, non-petaloid, 1½″ to 1¾″ long and Red Group 46B. The ovary is densely glandular-setose and has five locules. The capsule matures in about 5 months, in Independence, La., to about ¼″ to ½″ long; it has a persistent style, is Yellow-Green Group 147A, and contains from 100 to 400 nonwinged seeds. Normally fruit set is not heavy. There is a 2 to 3 week flowering period in April in Independence, La. Flowering resumes in July as the new buds mature and continues until frost which can be as late as November or December in Independence, La. Azaleas blooming at this time of year attract butterflies in profusion.

Culture: Grows well in a wide range of conditions, tolerates sun to shade. Prefers a moist, well-drained soil that is rich in organic matter. Responds well to mulching and medium applications of fertilizer; prefers ph 5.0 to 5.5. Very little pruning is needed; adaptable to container and above ground planters; makes a good foundation plant or informal hedge with excellent foliage and flower contrast. Ideal for coastal regions and warmer parts of Piedmont. Propagated with semi-hardwood cuttings in late spring through the summer.

Pests: Lace wing and spider mites can be a problem. 

I claim:
 1. A new and unique variety of Azalea plant named ‘Robleb’ as herein shown and described. 